The purpose of these experiments was to examine the role of the human cerebellum in the acquisition and retention of conditioned reflexes. Normal human subjects and patients with cerebellar lesions were tested for their capacity to acquire, retain and express conditioned eyeblink responses. In acquisition tests, subjects were trained in a delay classical conditioning paradigm using a tone conditioned stimulus and a midline forehead tap as an unconditioned stimulus. While normal subjects developed anticipatory eyeblinks to the tone in one session, patients with cerebellar lesions failed to acquire conditioned responses in four consecutive training sessions. The conditioning deficit was bilateral even in patients with a unilateral cerebellar pathology. The same groups of subjects were tested for the presence of eyeblinks to a visual threat. in these experiments, both normal subjects and patients with cerebellar lesions exhibited a high level of responding when they saw an object approaching their face. These eyeblinks to the visual threat are probably naturally acquired conditioned responses because they extinguish in normal subjects if they are not reinforced by the unconditioned cutaneous stimulus. in addition, the stimulus of seeing an approaching object blocks the acquisition of classically conditioned eyeblinks to a new conditioned stimulus in normal subjects. These data imply thar patients with cerebellar lesions who cannot acquire new classically conditioned responses are able to retain and express conditioned eyeblinks which were acquired before the onset of the pathology. Consequently cerebellum-dependent neural substrates which are involved in learning new conditioned reflexes do not seem to be required for the storage of naturally learned conditioned responses.

The role of conscious awareness in human Pavlovian conditioning was examined in 2 experiments using masked fear-relevant (snakes and spiders; Experiments 1 and 2) and fear-irrelevant (flowers and mushrooms; Experiment 1) pictures as conditioned stimuli, a mild electric shock as the unconditioned stimulus, and skin conductance responses as the primary dependent variable. The conditioned stimuli were presented briefly (30 ms) and were effectively masked by an immediately following masking stimulus. Experiment 1 demonstrated nonconscious conditioning to fear-relevant but not to fear-irrelevant stimuli. Even though the participants could not recognize the stimuli in Experiment 2, they differentiated between masked stimuli predicting and not predicting shocks in expectancy ratings. However, expectancy ratings were not related to the conditioned autonomic response.

THE retention of classical eyeblink conditioning was investigated in amnesic patients 10 days and 2 months after original learning. During reacquisition, the first CR occurred earlier and the CR frequencies during the first 10 trials were higher than in the baseline session. The overall CR rates increased significantly across sessions during both acquisition and extinction. The amnesics did not differ from matched controls on any of these effects, although they did not recall previous conditioning sessions and did not became fully aware of CS-US contingencies. (C) 1999 Lippincott Williams & Wilkins.

Knee-jerks to the sound of a bell were obtained from 6 college students after 150-238 trials, during which the 2 patellar tendons were struck 0.5 sec after the sound of the bell. These knee-jerks to the bell alone were not the result of S's voluntary effort, and attempts to inhibit the kicks were wholly unsuccessful. With increased numbers of paired stimulations, the regularity of responding to the bell alone was greatly increased, and the pattern of the knee-jerks was exactly the same as that of knee-jerks resulting from blows to the patellar tendon. The knee-jerks to the bell can be explained only in terms of reflex action, wherein repeated association of the functioning of the motor cells of the lumbar segment of the spinal cord with excitation of centers of the medulla resulting from the sound of the bell resulted in the development of an unusual reflex arc.
Notes
6 Ss. 150-238 trials until knee-jerks to sound of a bell. the two patellor tendons were struck 0.5 sec after bell. Twin lead hammers on both legs.
Lots of individual variation. After more trials regularity of responding to bell greatly increased. Responding was not the result of voluntary efforts, and attempts to inhibit responses were wholly unsuccesful. '..on the unanimous testimony of the subjects it was not produced voluntarily ie. there was noidea of the movement in consciousness, antecedent to the movement itself.' - he used special apparatus and chair at 45degrees with legs dangling.

Until half a century ago, associative learning played a fundamental role in theories of perceptual appearance [Berkeley, G. (1709) An Essay Towards a New Theory of Vision (Dublin), 1st Ed.]. But starting in 1955 [Gibson, J. J. & Gibson, E. J. (1955) Psychol. Rev. 62, 32-41], most studies of perceptual learning have not been concerned with association or appearance but rather with improvements in discrimination ability. Here we describe a "cue recruitment" experiment, which is a straightforward adaptation of Pavlov's classical conditioning experiment, that we used to measure changes in visual appearance caused by exposure to novel pairings of signals in visual stimuli. Trainees viewed movies of a rotating wire-frame (Necker) cube. This stimulus is perceptually bistable. On training trials, depth cues (stereo and occlusion) were added to force the perceived direction of rotation. Critically, an additional signal was also added, contingent on rotation direction. Stimuli on test trials contained the new signal but not the depth cues. Over 45 min, two of the three new signals that we tested acquired the ability to bias perceived rotation direction on their own. Results were consistent across the eight trainees in each experiment, and the new cue's effectiveness was long lasting. Whereas most adaptation aftereffects on appearance are opposite in direction to the training stimuli, these effects were positive. An individual new signal can be recruited by the visual system as a cue for the construction of visual appearance. Cue recruitment experiments may prove useful for reexamining of the role of experience in perception.
28 subjects, 2 or 3 daily sessions of 45-60min, 440-470 trials each session.